In recent years, an individual identification technology using wireless communication has attracted attention. In particular, as a semiconductor device which communicates data by wireless communication, an individual identification technology using an RFID (Radio Frequency Identification) tag has attracted attention. The RFID tag is also called an IC (Integrated Circuit) tag, an IC chip, an RF tag, a wireless tag, or an electronic tag. The individual identification technology using an RFID has started to help production, management, or the like of an individual object, and is anticipated to be applied to personal authentication.
RFIDs can be categorized into two types: an active RFID capable of transmitting an electromagnetic wave containing information of the RFID, and a passive RFID which drives utilizing power of an electromagnetic wave externally received, depending on whether it incorporates a power source or it is externally supplied with power (as for an active RFID, see Patent Document 1, and as for a passive RFID, see Patent Document 2). Among them, an active RFID is provided with a battery as a power source which supplies power for driving the RFID. Meanwhile, a passive RFID generates power for driving the RFID with the use of an external electromagnetic wave (carrier wave), and thus it is not provided with a battery.
Description is made of a specific structure of an active RFID with reference to a block diagram in FIG. 31. In an active RFID 3100 shown in FIG. 31, a communication signal received by an antenna circuit 3101 is inputted to a demodulation circuit 3105 and an amplifier 3106 in a signal processing circuit 3102. A communication signal is usually transmitted through a process such as ASK modulation or PSK modulation of a carrier of 13.56 MHz, 915 MHz, or the like. FIG. 31 shows an example of a case where 13.56 MHz is used for a communication signal. In FIG. 31, a clock signal as a reference is required for processing a signal. Here, a carrier of 13.56 MHz is used as a clock signal. The amplifier 3106 amplifies the carrier of 13.56 MHz and supplies it as a clock signal to a logic circuit 3107. Then, the communication signal subjected to ASK modulation or PSK modulation is demodulated in the demodulation circuit 3105. The modulated signal is transmitted to the logic circuit 3107 to be analyzed. The signal analyzed in the logic circuit 3107 is transmitted to a memory control circuit 3108 by which a memory circuit 3109 is controlled. Data stored in the memory circuit 3109 is transmitted to a logic circuit 3110. After being encoded in the logic circuit 3110, the signal is amplified in an amplifier 3111. By the signal, the modulation circuit 3112 modulates the carrier. Power for driving the RFID shown in FIG. 31 is supplied through a power source circuit 3104 by a battery 3103 provided outside the signal processing circuit. Then, the power source circuit 3104 supplies power to the amplifier 3106, the demodulation circuit 3105, the logic circuit 3107, the memory control circuit 3108, the memory circuit 3109, the logic circuit 3110, the amplifier 3111, the modulation circuit 3112, and the like. Thus, an active RFID operates.
Description is made of a specific structure of a passive RFID with reference to a block diagram in FIG. 32. In a passive RFID 3200 shown in FIG. 32, a communication signal received by an antenna circuit 3201 is inputted to a demodulation circuit 3205 and an amplifier 3206 in a signal processing circuit 3202. A communication signal is usually transmitted through a process such as ASK modulation or PSK modulation by a carrier of 13.56 MHz, 915 MHz, or the like. FIG. 32 shows an example of a case where 13.56 MHz is used for a communication signal. In FIG. 32, a clock signal as a reference is required for processing a signal. Here, a carrier of 13.56 MHz is used as a clock signal. The amplifier 3206 amplifies the carrier of 13.56 MHz and supplies it as a clock signal to a logic circuit 3207. Then, the communication signal subjected to ASK modulation or PSK modulation is demodulated in the demodulation circuit 3205. The modulated signal is transmitted to the logic circuit 3207 to be analyzed. The signal analyzed in the logic circuit 3207 is transmitted to a memory control circuit 3208 by which a memory circuit 3209 is controlled. Data stored in the memory circuit 3209 is transmitted to a logic circuit 3210. After being encoded in the logic circuit 3210, the signal is amplified in an amplifier 3211. By the signal, the modulation circuit 3212 modulates the carrier. Meanwhile, a communication signal inputted into a rectifier circuit 3203 is rectified, which is inputted to a power source circuit 3204. The power source circuit 3204 supplies power to the amplifier 3206, the demodulation circuit 3205, the logic circuit 3207, the memory control circuit 3208, the memory circuit 3209, the logic circuit 3210, the amplifier 3211, the modulation circuit 3212, and the like. Thus, a passive RFID operates.    [Patent Document 1] Japanese Published Patent Application No. 2005-316724    [Patent Document 2] Japanese Translation of PCT International Application No. 2006-503376